Ionic liquids as selective additives for separation of close-boiling or azeotropic mixtures

ABSTRACT

The invention relates to a process for separating close-boiling, homo- and heteroazeotropic mixtures by using ionic liquids. Due to the selectivity and unusual combination of properties of the ionic liquids the process is superior to conventional extractive rectification from the point of view of costs and energy.

DESCRIPTION

[0001] The invention relates to a process and a method for separatingclose-boiling or azeotropic mixtures by using ionic liquids as selectiveadditives in rectification.

[0002] Numerous liquid mixtures occur in industry which cannot beseparated by conventional rectification but rather are preferablyseparated by extractive rectification [Stichlmair, S. and Fair, J.,Distillation, ISBN 0-471-25241-7, page 241 et seq.]. This state ofaffairs is due to the similar boiling behavior of the components of themixture, that is to say their property of distributing themselvesbetween the vapor and liquid phase in almost or exactly equimolarproportions at a defined pressure and a defined temperature.

[0003] The effort of separating a binary liquid mixture composed of thecomponents i and j by rectification is reflected in what is known as theseparation factor α_(ij), the distribution coefficient of components iand j. The closer the separation factor approaches the value one themore effort the separation of the components of the mixture byconventional rectification requires, since either the number oftheoretical plates in the distillation column and/or the reflux ratio atthe top of the column must be increased. If the separation factorassumes the value one an azeotropic point is reached and furtherenrichment of the components of the mixture is no longer possible, evenif the number of theoretical plates or the reflux ratio is increased. Ingeneral when making use of the separation factor it has to be borne inmind that it can be greater than or less than 1 depending on whether thedistribution coefficient of the low boiler is in the numerator or in thedenominator. Normally the low boiler is placed in the numerator so thatthe separation factor is great than 1.

[0004] A procedure frequently employed in industry for separatingclose-boiling systems—by which is meant a separation factor less than1.2 for instance—or azeotropic systems involves adding a selectiveadditive, commonly referred to as the entrainer, to an extractiverectification. A suitable additive influences the separation factor byselective interaction with one or more of the components of the mixtureso that separation of the close-boiling or azeotropically boilingcomponents of the mixture is made possible. In extractive rectificationthe components obtained at the top and bottom of the column due to theaction of the entrainer are the target components for the column.

[0005] A measure of the intensity of the interactions of the entrainerwith one or more of the components of the mixture is provided by what isknown as selectivity. Selectivity is defined as the ratio of thelimiting activity coefficient of component i to the limiting activitycoefficient of component j, components i and j being present at aninfinite degree of dilution in the entrainer [Schult, C. J. et. al.;Infinite-dilution activity coefficients for several solutes inhexadecane and in n-methyl-2-pyrrolidone (NMP): experimentalmeasurements and UNIFAC predictions; Fluid Phase Equilibria 179 (2001)pp.117-129]. As expounded by Schult et. al., a higher entrainerselectivity results in a higher relative volatility, a lower refluxratio and hence in lower separating costs. As disclosed later on, theaim is to achieve as high a selectivity as possible, e.g. greater than1.3, preferably greater than 2.0.

[0006] The surprising discovery of the suitability of some ionic liquidsfor the separation of azeotropic and/or close-boiling mixtures on thebasis of the entrainer selectivity and of the separation factor is shownbelow. The activity coefficients playing a key role in entrainerselectivity at infinite dilution can be determined by a variety ofmethods, preferably by using gas-liquid chromatography (GLC or GLPC)[Schult, C. J. et. al.; Infinite-dilution activity coefficients forseveral solutes in hexadecane and in n-methyl-2-pyrrolidone (NMP):experimental measurements and UNIFAC predictions; Fluid Phase Equilibria179 (2001) pp.117-129] and equations (4) and (6) used in the latterpublication by Schult et. al.

[0007] On grounds of costs, the aim is to minimize the amount ofadditive to be employed. The entrainer is advantageously presentsubstantially in the liquid phase in the column. Large volumes mightresult in an enlargement of the column diameter but would always giverise to an increased pressure loss in the vapor phase in the column andhence also to a greater energy loss.

[0008] Accordingly, an increase in the quantity of entrainer results inincreased capital and operating costs.

[0009] For a given column length and the same reflux ratio the higherseparation factor yields a purer product or for a given column lengthand degree of purity of the overhead product the higher separationfactor results in a lower reflux ratio and hence in energy savings. Fora given degree of purity and a given reflux ratio an increase in thequantity of entrainer and a higher separation factor results in savingsin capital costs due to shortening of the length of the column. By thesemeans the design engineer has the power to minimize capital or runningcosts (energy costs) on the basis of circumstances specific to the site.

[0010] The invention relates to a process and a method in which a novelclass of substances, ionic liquids, is employed for separatingclose-boiling or azeotropic liquid mixtures since these ionic liquidsare surprisingly superior to the conventional additives. The superioritycan be seen directly in the selectivity and separation factor. When asuitable ionic liquid is used the separation factor at the azeotropicpoint is further removed from the value of one than is the case whenequivalent quantities of a conventional additive are used.

[0011] By ionic liquids is meant those defined by Wasserscheid and Keimin Angewandte Chemie 2000, 112, 3926-3945. The ionic liquids group ofsubstances represents a new type of solvent. As set out in the abovepublication ionic liquids are salts of nonmolecular, ionic nature whichmelt at relatively low temperatures. They are already in the moltenstate at relatively low temperatures less than 200° C., preferably lessthan 150° C., particularly preferably less than 100° C. and at the sametime are of relatively low viscosity. They are highly soluble in a largenumber of organic, inorganic and polymeric substances.

[0012] By comparison with ionic salts, ionic liquids are molten atsubstantially lower temperatures (below 200° C. as a rule) and oftenhave a melting point below 0° C., in some cases down to −96° C., whichis important for the industrial implementation of extractiverectification.

[0013] Moreover, ionic liquids are usually nonflammable, noncorrosive,of low viscosity and are exceptional by having an immeasurable vaporpressure.

[0014] Compounds designated according to the invention as ionic liquidsare those which have at least one positive and at least one negativecharge but are overall neutral in charge and have a melting point below200° C., preferably below 100, particularly preferably below 50° C.

[0015] Ionic liquids can also exhibit a plurality of positive ornegative charges, for example 1 to 5, preferably 1 to 4, particularlypreferably 1 to 3, very particularly preferably 1 to 2, but inparticular one negative and one positive charge each.

[0016] The charges may be found at various localized or delocalizedregions inside a molecule, that is to say like betaine, or bedistributed in each case over a separate anion and cation. Those ionicliquids are preferred which are built up out of at least one cation andat least one anion. As stated above, the cation and anion may be singlyor multiply charged, preferably singly charged.

[0017] Of course mixtures of different ionic liquids are alsoconceivable.

[0018] Preferred cations are ammonium or phosphonium ions or thosecations containing at least a five- to six-membered heterocyclepossessing at least one phosphorus or nitrogen atom and optionally anoxygen or sulfur atom, particularly preferably those compoundscontaining at least one five- to six-membered heterocycle possessingone, two or three nitrogen atoms and a sulfur or an oxygen atom, veryparticularly preferably those having one or two nitrogen atoms.

[0019] Particularly preferred ionic liquids are those having a molecularweight of less than 1,000 g/mol, very particularly preferably less than350 g/mol.

[0020] Furthermore those cations are preferred which are selected fromcompounds of the formulae (Ia) to (Iw):

[0021] as well as oligopolymers or polymers containing these structures,

[0022] where

[0023] R¹, R², R³, R⁴, R⁵, R⁶ and R⁷ independently of one another eachstand for C₁-C₁₈ alkyl, C₂-C₁₈ alkyl optionally interrupted by one ormore oxygen and/or sulfur atoms and/or one or more substituted orunsubstituted imino groups, C₆-C₁₂ aryl, C₅-C₁₂ cycloalkyl or a five- tosix-membered heterocycle possessing oxygen, nitrogen and/or sulfuratoms, or two of them jointly form an unsaturated, saturated or aromaticring optionally interrupted by one or more oxygen and/or sulfur atomsand/or one or more substituted or unsubstituted imino groups, whereinsaid residues can each be substituted by functional groups, aryl, alkyl,aryloxy, alkyloxy, halogen, hetero atoms and/or heterocycles.

[0024] R¹, R², R³, R⁴, R⁵ and R⁶ can additionally represent hydrogen.

[0025] Moreover, R⁷ can stand for C₁-C₁₈ alkyloyl (alkylcarbonyl),C₁-C₁₈-alkyloxycarbonyl, C₅-C₁₂ cycloalkylcarbonyl or C₆-C₁₂ aryloyl(arylcarbonyl), wherein said residues can be substituted by functionalgroups, aryl, alkyl, aryloxy, alkyloxy, halogen, hetero atoms and/orheterocycles.

[0026] Therein

[0027] C₁-C₁₈ alkyl optionally substituted by functional groups, aryl,alkyl, aryloxy, alkyloxy, halogen, hetero atoms and/or heterocyclesstands by way of example for methyl, ethyl, propyl, isopropyl, n-butyl,sec-butyl, tert-butyl, pentyl, hexyl, heptyl, octyl, 2-ethylhexyl,2,4,4-trimethylpentyl, decyl, dodecyl, tetradecyl, heptadecyl,octadecyl, 1,1-dimethylpropyl, 1,1-dimethylbutyl,1,1,3,3-tetramethylbutyl, benzyl, 1-phenylethyl, 2-phenylethyl,α,α-dimethylbenzyl, benzhydryl, p-tolylmethyl, 1-(p-butylphenyl)ethyl,p-chlorobenzyl, 2,4-dichlorobenzyl, p-methoxybenzyl, m-ethoxybenzyl,2-cyanoethyl, 2-cyanopropyl, 2-methoxycarbonylethyl,2-ethoxycarbonylethyl, 2-butoxycarbonylpropyl,1,2-di-(methoxycarbonyl)ethyl, 2-methoxyethyl, 2-ethoxyethyl,2-butoxyethyl, diethoxymethyl, diethoxyethyl, 1,3-dioxolan-2-yl,1,3-dioxan-2-yl, 2-methyl-1,3-dioxolan-2-yl, 4-methyl-1,3-dioxolan-2-yl,2-isopropoxyethyl, 2-butoxypropyl, 2-octyloxyethyl, chloromethyl,2-chloroethyl, trichloromethyl, trifluoromethyl,1,1-dimethyl-2-chloroethyl, 2-methoxyisopropyl, 2-ethoxyethyl,butylthiomethyl, 2-dodecylthioethyl, 2-phenylthioethyl,2,2,2-trifluoroethyl, 2-hydroxyethyl, 2-hydroxypropyl, 3-hydroxypropyl,4-hydroxybutyl, 6-hydroxyhexyl, 2-aminoethyl, 2-aminopropyl,3-aminopropyl, 4-aminobutyl, 6-aminohexyl, 2-methylaminoethyl,2-methylaminopropyl, 3-methylaminopropyl, 4-methylaminobutyl,6-methylaminohexyl, 2-dimethylaminoethyl, 2-dimethylaminopropyl,3-dimethylaminopropyl, 4-dimethylaminobutyl, 6-dimethylaminohexyl,2-hydroxy-2,2-dimethylethyl, 2-phenoxyethyl, 2-phenoxypropyl,3-phenoxypropyl, 4-phenoxybutyl, 6-phenoxyhexyl, 2-methoxyethyl,2-methoxypropyl, 3-methoxypropyl, 4-methoxybutyl, 6-methoxyhexyl,2-ethoxyethyl, 2-ethoxypropyl, 3-ethoxypropyl, 4-ethoxybutyl or6-ethoxyhexyl and,

[0028] C₂-C₁₈ alkyl optionally interrupted by one or more oxygen and/orsulfur atoms and/or one or more substituted or unsubstituted iminogroups stands by way of example for 5-hydroxy-3-oxapentyl,8-hydroxy-3,6-dioxaoctyl, 11-hydroxy-3,6,9-trioxaundecyl,7-hydroxy-4-oxa-heptyl, 11-hydroxy-4,8-dioxaundecyl,15-hydroxy-4,8,12-trioxapentadecyl, 9-hydroxy-5-oxa-nonyl,14-hydroxy-5,10-oxatetradecyl, 5-methoxy-3-oxapentyl,8-methoxy-3,6-dioxaoctyl, 11-methoxy-3,6,9-trioxaundecyl,7-methoxy-4-oxaheptyl, 11-methoxy-4,8-dioxaundecyl,15-methoxy-4,8,12-trioxapentadecyl, 9-methoxy-5-oxanonyl,14-methoxy-5,10-oxatetradecyl, 5-ethoxy-3-oxapentyl,8-ethoxy-3,6-dioxaoctyl, 11-ethoxy-3,6,9-trioxaundecyl,7-ethoxy-4-oxa-heptyl, 11-ethoxy-4,8-dioxaundecyl,15-ethoxy-4,8,12-trioxapentadecyl, 9-ethoxy-5-oxa-nonyl or14-ethoxy-5,10-oxatetradecyl.

[0029] If two radicals form a ring these radicals may jointly stand for1,3-propylene, 1,4-butylene, 2-oxa-1,3-propylene, 1-oxa-1,3-propylene,2-oxa-1,3-propylene, 1-oxa-1,3-propenylene, 1-aza-1,3-propenylene,1-(C₁-C₄ alkyl)-1-aza-1,3-propenylene, 1,4-buta-1,3-dienylene,1-aza-1,4-buta-1,3-dienylene or 2-aza-1,4-buta-1,3-dienylene.

[0030] The number of oxygen and/or sulfur atoms and/or imino groups isnot limited. In general there are no more than 5 in the radical,preferably no more than 4 and very particularly preferably no more than3.

[0031] Furthermore, between two hetero atoms there is usually at leastone carbon atom, preferably at least two.

[0032] Substituted and unsubstituted imino groups can be by way ofexample imino, methylimino, iso-propylimino, n-butylimino ortert-butylimino.

[0033] Furthermore,

[0034] functional groups stands for carboxy, carboxamido, hydroxy,di-(C₁-C₄ alkyl)-amino, C₁-C₄ alkyloxycarbonyl, cyano or C₁-C₄ alkyloxy,

[0035] C₆-C₁₂ aryl optionally substituted by functional groups, aryl,alkyl, aryloxy, alkyloxy, halogen, hetero atoms and/or heterocyclesstands by way-of example for phenyl, tolyl, xylyl, α-naphthyl,β-naphthyl, 4-diphenylyl, chlorophenyl, dichlorophenyl, trichlorophenyl,difluorophenyl, methylphenyl, dimethylphenyl, trimethylphenyl,ethylphenyl, diethylphenyl, iso-propylphenyl, tert-butylphenyl,dodecylphenyl, methoxyphenyl, dimethoxyphenyl, ethoxyphenyl,hexyloxyphenyl, methylnaphthyl, isopropylnaphthyl, chloronoaphthyl,ethoxynaphthyl, 2,6-dimethylphenyl, 2,4,6-trimethylphenyl,2,6-dimethoxyphenyl, 2,6-dichlorophenyl, 4-bromophenyl, 2- or4-nitrophenyl, 2,4- or 2,6-dinitrophenyl, 4-dimethylaminophenyl,4-acetylphenyl, ethoxyethylphenyl or ethoxymethylphenyl,

[0036] C₅-C₁₂ cycloalkyl optionally substituted by functional groups,aryl, alkyl, aryloxy, alkyloxy, halogen, hetero atoms and/orheterocycles stands by way of example for cyclopentyl, cyclohexyl,cyclooctyl, cyclododecyl, methylcyclopentyl, dimethylcyclopentyl,methylcyclohexyl, dimethylcyclohexyl, diethylcyclohexyl,butylcyclohexyl, methoxycyclohexyl, dimethoxycyclohexyl,diethoxycyclohexyl, butylthiocyclohexyl, chlorocyclohexyl,dichlorocyclohexyl, dichlorocyclopentyl as well as a saturated orunsaturated bicyclic system such as norbornyl or norbornenyl forexample,

[0037] a five- to six-membered heterocycle possessing oxygen, nitrogenand/or sulfur atoms stands by way of example for furyl, thiophenyl,pyrryl, pyridyl, indolyl, benzoxazolyl, dioxolyl, dioxyl,benzimidazolyl, benzthiazolyl, dimethylpyridyl, methylquinolyl,dimethylpyrryl, methoxyfuryl, dimethoxypyridyl, difluoropyridyl,methylthiophenyl, isopropylthiophenyl or tert-butylthiophenyl and

[0038] C₁ to C₄ alkyl stands by way of example for methyl, ethyl,propyl, isopropyl, n-butyl, sec-butyl or tert-butyl.

[0039] C₁-C₁₈ alkyloyl (alkylcarbonyl) can be by way of example acetyl,propionyl, n-butyloyl, sec-butyloyl, tert-butyloyl,2-ethylhexylcarbonyl, decanoyl, dodecanoyl, chloroacetyl,trichloroacetyl or trifluoroacetyl.

[0040] C₁-C₁₈-alkyloxycarbonyl can be by way of examplemethyloxycarbonyl, ethyloxycarbonyl, propyloxycarbonyl,isopropyloxycarbonyl, n-butyloxycarbonyl, sec-butyloxycarbonyl,tert-butyloxycarbonyl, hexyloxycarbonyl, 2-ethylhexyloxycarbonyl orbenzyloxycarbonyl.

[0041] C₅-C₁₂ cycloalkylcarbonyl can be by way of examplecyclopentylcarbonyl, cyclohexylcarbonyl or cyclododecylcarbonyl.

[0042] C₆-C₁₂ aryloyl (arylcarbonyl) can be by way of example benzoyl,toluyl, xyloyl, α-naphthoyl, β-naphthoyl, chlorobenzoyl,dichlorobenzoyl, trichlorobenzoyl or trimethylbenzoyl.

[0043] R¹, R², R³, R⁴, R⁵ and R⁶ independently of one another arepreferably hydrogen, methyl, ethyl, n-butyl, 2-hydroxyethyl,2-cyanoethyl, 2-(methoxycarbonyl)ethyl, 2-(ethoxycarbonyl)-ethyl,2-(n-butoxycarbonyl)ethyl, dimethylamino, diethylamino and chlorine.

[0044] R⁷ is preferably methyl, ethyl, n-butyl, 2-hydroxyethyl,2-cyanoethyl, 2-(methoxycarbonyl)-ethyl, 2-(ethoxycarbonyl)ethyl,2-(n-butoxycarbonyl)ethyl, acetyl, propionyl, t-butyryl,methoxycarbonyl, ethoxycarbonyl or n-butoxycarbonyl.

[0045] Particularly preferred pyridinium ions (Ia) are those in whichone of the radicals R¹ to R⁵ is methyl, ethyl or chlorine, R⁷ is acetyl,methyl, ethyl or n-butyl and all others are hydrogen, or R³ isdimethylamino, R⁷ acetyl, methyl, ethyl or n-butyl and all others arehydrogen, or R⁷ is acetyl, methyl, ethyl or n-butyl and all others arehydrogen, or R² is carboxy or carboxamido, R⁷ acetyl, methyl, ethyl orn-butyl and all others are hydrogen, or R¹ and R² or R² and R³ are1,4-buta-1,3-dienylene, R⁷ acetyl, methyl, ethyl or n-butyl and allothers are hydrogen.

[0046] Particularly preferred pyridazinium ions (Ib) are those in whichOne of the groups R¹ to R⁴ is methyl or ethyl, R⁷ is acetyl, methyl,ethyl or n-butyl and all others are hydrogen, or R⁷ is acetyl, methyl,ethyl or n-butyl and all others are hydrogen.

[0047] Particularly preferred pyrimidinium ions (Ic) are those in whichR² to R⁴ are hydrogen or methyl, R⁷ is acetyl, methyl, ethyl or n-butyland R¹ is hydrogen, methyl or ethyl, or R² and R⁴ are methyl, R³ ishydrogen and R¹ is hydrogen, methyl or ethyl and R⁷ is acetyl, methyl,ethyl or n-butyl.

[0048] Particularly preferred pyrazinium ions (Id) are those in which

[0049] R¹ to R⁴ are all methyl and

[0050] R⁷ is acetyl, methyl, ethyl or n-butyl, or R⁷ is acetyl, methyl,ethyl or n-butyl and all others are hydrogen.

[0051] Particularly preferred imidazolium ions (Ie) are those in whichindependently of one another

[0052] R¹ is selected from methyl, ethyl, n-propyl, n-butyl, n-pentyl,n-octyl, n-decyl, n-dodecyl, 2-hydroxyethyl or 2-cyanoethyl,

[0053] R⁷ is acetyl, methyl, ethyl or n-butyl and

[0054] R² to R⁴ independently of one another stand for hydrogen, methylor ethyl.

[0055] Particularly preferred 1H-pyrazolium ions (If) are those in whichindependently of one another

[0056] R¹ is selected from hydrogen, methyl or ethyl,

[0057] R², R³ and R⁴ from hydrogen or methyl and

[0058] R⁷ from acetyl, methyl, ethyl or n-butyl.

[0059] Particularly preferred 3H-pyrazolium ions (Ig) are those in whichindependently of one another

[0060] R¹ is selected from hydrogen, methyl or ethyl,

[0061] R², R³ and R⁴ from hydrogen or methyl and

[0062] R⁷ from acetyl, methyl, ethyl or n-butyl.

[0063] Particularly preferred 4H-pyrazolium ions (Ih) are those in whichindependently of one another

[0064] R¹ to R⁴ are selected from hydrogen or methyl and

[0065] R⁷ from acetyl, methyl, ethyl or n-butyl.

[0066] Particularly preferred 1-pyrazolinium ions (Ii) are those inwhich independently of one another

[0067] R¹ to R⁶ are selected from hydrogen or methyl and

[0068] R⁷ from acetyl, methyl, ethyl or n-butyl.

[0069] Particularly preferred 2-pyrazolinium ions (Ij) are those inwhich independently of one another

[0070] R¹ is selected from hydrogen, methyl, ethyl or phenyl,

[0071] R⁷ from acetyl, methyl, ethyl or n-butyl and

[0072] R² to R⁶ from hydrogen or methyl.

[0073] Particularly preferred 3-pyrazolinium ions (Ik) are those inwhich independently of one another

[0074] R¹ or R² is selected from hydrogen, methyl, ethyl or phenyl,

[0075] R⁷ from acetyl, methyl, ethyl or n-butyl and

[0076] R³ to R⁶ from hydrogen or methyl.

[0077] Particularly preferred imidazolinium ions (Il) are those in whichindependently of one another

[0078] R¹ or R² is selected from hydrogen, methyl, ethyl, n-butyl orphenyl,

[0079] R⁷ from acetyl, methyl, ethyl or n-butyl and

[0080] R³ or R⁴ from hydrogen, methyl or ethyl and

[0081] R⁵ or R⁶ from hydrogen or methyl.

[0082] Particularly preferred imidazolinium ions (Im) are those in whichindependently of one another

[0083] R¹ or R² is selected from hydrogen, methyl or ethyl,

[0084] R⁷ from acetyl, methyl, ethyl or n-butyl and

[0085] R³ to R⁶ from hydrogen or methyl.

[0086] Particularly preferred imidazolinium ions (In) are those in whichindependently of one another

[0087] R¹, R² or R³ is selected from hydrogen, methyl or ethyl,

[0088] R⁷ from acetyl, methyl, ethyl or n-butyl and

[0089] R⁴ to R⁶ from hydrogen or methyl.

[0090] Particularly preferred thiazolium ions (Io) or oxazolium ions(Ip) are those in which independently of one another

[0091] R¹ is selected from hydrogen, methyl, ethyl or phenyl,

[0092] R⁷ from acetyl, methyl, ethyl or n-butyl and

[0093] R² or R³ from hydrogen or methyl.

[0094] Particularly preferred 1,2,4-triazolium ions (Iq) and (Ir) arethose in which independently of one another

[0095] R¹ or R² is selected from hydrogen, methyl, ethyl or phenyl,

[0096] R⁷ from acetyl, methyl, ethyl or n-butyl and

[0097] R³ from hydrogen, methyl or phenyl.

[0098] Particularly preferred 1,2,3-triazolium ions (Is) and (It) arethose in which independently of one another

[0099] R¹ is selected from hydrogen, methyl or ethyl,

[0100] R⁷ from acetyl, methyl, ethyl or n-butyl and

[0101] R² or R³ from hydrogen or methyl, or

[0102] R² and R³ are 1,4-buta-1,3-dienylene and all others are hydrogen.

[0103] Particularly preferred pyrrolidinium ions (Iu) are those in whichindependently of one another

[0104] R¹ and R⁷ are selected from acetyl, methyl, ethyl or n-butyl and

[0105] R², R³, R⁴ and R⁵ stand for hydrogen.

[0106] Particularly preferred ammonium ions (Iv) are those in whichindependently of one another

[0107] R⁷ is selected from acetyl, methyl, ethyl or n-butyl and

[0108] R¹, R², and R³ from methyl, ethyl, n-butyl, 2-hydroxyethyl,benzyl or phenyl.

[0109] Particularly preferred phosphonium ions (Iw) are those in whichindependently of one another

[0110] R⁷ is selected from acetyl, methyl, ethyl or n-butyl and R¹, R²,and R³ from phenyl, phenoxy, ethoxy and n-butoxy.

[0111] Among these the ammonium, phosphonium, pyridinium and imidazoliumions are preferred.

[0112] Very particularly preferred as cations are1,2-dimethylpyridinium, 1-methyl-2-ethylpyridinium,1-methyl-2-ethyl-6-methylpyridinium, N-methylpyridinium,1-butyl-2-methylpyridinium, 1-butyl-2-ethylpyridinium,1-butyl-2-ethyl-6-methylpyridinium, N-butylpyridinium,1-butyl-4-methylpyridinium, 1,3-dimethylimidazolium,1,2,3-trimethylimidazolium, 1-n-butyl-3-methylimidazolium,1,3,4,5-tetramethylimidazolium, 1,3,4-trimethylimidazolium,2,3-dimethylimidazolium, 1-butyl-2,3-dimethylimidazolium,3,4-dimethylimidazolium, 2-ethyl-3,4-dimethylimidazolium,3-methyl-2-ethylimidazol, 3-butyl-1-methylimidazolium,3-butyl-1-ethylimidazolium, 3-butyl-1,2-dimethylimidazolium,1,3-di-n-Butylimidazolium, 3-butyl-1,4,5-trimethylimidazolium,3-butyl-1,4-dimethylimidazolium, 3-butyl-2-methylimidazolium,1,3-dibutyl-2-methylimidazolium, 3-butyl-4-methylimidazolium,3-butyl-2-ethyl-4-methylimidazolium and 3-butyl-2-ethylimidazolium,1-methyl-3-octylimidazolium and 1-decyl-3-methylimidazolium.

[0113] Particularly preferred are 1-butyl-4-methylpyridinium,1-n-butyl-3-methylimidazolium and 1-n-butyl-3-ethylimidazolium,

[0114] For the anions, all anions are conceivable in principle.

[0115] Preferred anions are halides, F—, Cl—, Br—, I—, acetate CH₃COO—,trifluoroacetate CF₃COO—, triflate CF₃SO₃—, sulfate SO₄ ²—,hydrogensulfate HSO₄—, methylsulfate CH₃OSO₃—, ethylsulfate C₂H₅OSO₃—,sulfite SO₃ ²—, hydrogensulfite HSO₃—, chloroaluminates AlCl₄—, Al₂Cl₇—,Al₃Cl₁₀—, tetrabromoaluminate AlBr₄—, nitrite NO₂—, nitrate NO₃—,chlorocuprate CuCl₂—, phosphate PO₄ ³—, hydrogenphosphate HPO₄ ²—,dihydrogenphosphate H₂PO₄—, carbonate CO₃ ² and hydrogencarbonate HCO₃—.

[0116] Particularly preferred tetrafluoroborate BF₄—,hexafluorophosphate PF₆—, bis(trifluoromethylsulfonyl)imide (CF₃SO₂)₂N—and tosylate p-CH₃C₆H₄SO₃—.

[0117] Ionic liquids which are very particularly preferred are thosewhose salts exhibit an E_(T)(30) value of >20, preferably of >30,particularly preferably of >40. The E_(T)(30) value is a measure ofpolarity and is described by C. Reichardt in Reichardt, Christian,Solvent Effects in Organic Chemistry, Weinheim: VCH, 1979-XI,(Monographs in Modern Chemistry 3), ISBN 3-527-25793-4, page 241.

[0118] The change in separation factor brought about by the entrainercan be determined by a number of methods, preferably by headspaceanalysis as published by Hachenberg and Schmidt in Verfahrenstechnik,8(1974), 12, pages 343-347. In determining the effect of the entraineron the mixture to be separated (the feed) calculation is generally doneon an entrainer-free basis, that is to say that although theconcentration of the entrainer in the liquid mixture is noted it is nottaken into account in the percentage statement of the concentrations ofthe target components.

[0119] Suitable ionic liquids are those which at a total concentrationin the liquid of 5 to 90 mol %, preferably 10 to 70 mol %, result in achange in the separation factor of the target components relative to oneanother different from one. This change can be determined in thedescribed headspace analysis.

[0120] The ionic liquid acting as entrainer is selected so that

[0121] it has as high a selectivity as possible,

[0122] it dissolves homogeneously to a concentration of at least 5 mol %in the mixture of substances to be separated,

[0123] it does not undergo any chemical reaction involving rupture ofcovalent bonds with either of the components of the mixture ofsubstances to be separated,

[0124] the components of the bottom product can be separated from theentrainer at low cost by evaporation due to the supply of heat and/orreduction of pressure or rectification or extraction or stripping usinginert gas or conversion into a solid phase.

[0125] In the rectification column it is not possible to adjust aconstant concentration of the ionic fluid over the entire height of thecolumn. On the contrary, in the enriching section directly below thepoint of addition of the ionic fluid a higher concentration will set inby comparison with the stripping section below the feed inlet. Thequantified value of 5-90 mol % should be measured directly on the feedplate for the ionic fluid. In this way a suitable concentration would beensured in the enriching section, that. is to say just where theazeotrope is to be broken down.

[0126] In order to ensure that the ionic liquid dissolves well in themixture to be separated the forces of attraction between the moleculesof the ionic liquid should be approximately just as great as thosebetween the molecules of the feed. In this case the intermolecularforces in operation are ionic forces, dipole-dipole forces, inductionforces, dispersion forces and hydrogen bonds, cf. Ullmann's Encyclopediaof Industrial Chemistry (1993), Vol. A24, pp. 438-439. It is possible toadjust these forces in the ionic liquids by varying the cations. In thisway solubility properties can be regulated. Thus, for example, bylengthening the chain of the alkyl residue on an alkylmethylimidazoliumtetrafluoroborate the water-repelling properties increase and hencemiscibility with water decreases. This adjustment of salvation strengthis particularly effective in relation to aliphatics, cf. H.Waffenschmidt, Dissertation, RWTH Aachen, 2000. The anion also has aneffect on dissolving characteristics. Criteria for estimating thedissolving behavior of an ionic liquid are the dielectric constant ofthe ionic liquid and of the feed and the polarity of the mixture.

[0127] An embodiment of extractive rectification in a process isillustrated by FIG. 1. “2” is the inflow of the entrainer into acountercurrent rectification column. Since in conventional processes theentrainer has a slight but appreciable volatility relative to the topproduct (stream 7) separative elements “1” must be used for separationbetween the top product and entrainer. The separative elements “3” and“5” bring about the desired separation between overhead product andbottom product under the action of the entrainer, stream “4” is theinflow of the components to be separated (feed) and stream “6” is bottomproduct and the entrainer. Separative elements can be by way of exampleplates or ordered or disordered packings.

[0128] The process according to the invention has the advantage that—asmentioned above—the vapor pressure of the pure ionic liquid and hencealso its partial pressure in the mixture with the top product isapproximately equal to zero. Accordingly, in the process according tothe invention the separative elements “1” may be dispensed with.

[0129] The ionic fluid is added preferably in the enriching sectionclose to the top of the column, particularly preferably in the uppermost3 stages, very particularly preferably in the uppermost stage below thecondenser.

[0130] A further advantage of the process according to the inventionwith ionic liquid as entrainer is that in order to separate theentrainer from the bottom product various separating operations may beused. Advantageous embodiments are:

[0131] Regeneration of the entrainer by simple evaporation.

[0132] Since the vapor pressure of the pure entrainer and hence also itspartial pressure in the mixture with the bottom product is approximatelyequal to zero, an evaporation process can be run continuously ordiscontinuously without further separative elements. Thin filmevaporators such as falling-film or rotary evaporators are particularlysuitable for continuous evaporation. In discontinuous concentrationprocesses two evaporator stages are run alternately so that regeneratedionic liquid can be fed continuously to the extractive rectificationcolumn.

[0133] Regeneration of the entrainer by means of a stripping columnSince the vapor pressure of the pure entrainer and hence also itspartial pressure in the mixture with the bottom product is equal to zerothe entrainer cannot be completely freed of bottom product in thecountercurrent process by evaporation alone. In an advantageousembodiment hot gas is conveyed in a stripping column in countercurrentflow relative to a mixture of bottom product and entrainer.

[0134] Many ionic liquids are notable for crystallization or glasstransition temperatures which are well below 0° C. In these casesparticularly simple, low-cost separation and recirculation of the ionicliquid is possible by precipitation to form a solid phase. The bottomproduct is then obtained in solid form while the entrainer can bereturned as the pure substance to the extractive rectification process.Precipitation can be carried out in accordance with the teachings ofcooling crystallization, evaporative crystallization or vacuumcrystallization. If the freezing point of the entrainer is above thefreezing point of the bottom product in a variant of this method theentrainer is obtained as the solid phase and the bottom product as theliquid phase.

[0135] The use of ionic fluids as entrainers in extractive rectificationis particularly suitable inter alia for the following applications, e.g.azeotropes: amines/water, THF/water, formic acid/water, alcohols/water,acetone/methanol, acetate/water, acrylate/water or close-boilingmixtures: acetic acid/water, C4 hydrocarbons, C3 hydrocarbons,alkanes/alkenes.

[0136] For the following reasons the process according to the inventionis a substantial improvement over the processes in the literature forconventional extractive rectification.

[0137] Ionic liquids are more selective than traditional entrainers. Dueto their high selectivity by comparison with conventional extractiverectification they allow a lower mass flow rate of entrainer to be fedin extractive rectification and/or the number of separation stages inthe extractive rectification column to be reduced.

[0138] Due to the extremely low vapor pressure of the entrainer variousseparation operations can be used to separate the entrainer from thebottom product which by comparison with the second rectification columnin conventional extractive rectification afford an advantage in terms ofrunning and capital costs.

[0139] The separative elements “1” in conventional extractiverectification result in separation of the entrainer from the overheadproduct, but separation is never complete. Discharge of portions ofionic liquid via the vapor phase without the separative elements “1” isnot possible due to its extremely low volatility.

[0140] Capital costs are reduced because the separative elements “1” arenot needed.

[0141] The process according to the invention is explained below bymeans of examples.

EXAMPLE 1 System to be Separated: Butene-butane

[0142] According to the literature [Gmehling, J, Onken, U and Arlt, WVapor-Liquid Equilibrium Data Collection, Dechema Data Series, Vol. IPart 6a, p. 17] the butene-butane system is a close-boiling system. Theseparation factor which was measured by means of gas-liquidchromatography (GLC) at infinite dilution of butane and butene in theionic liquid octylmethylimidazolium tetrafluoroborate (OMIM-BF₄) at 70°C. is 0.74.

[0143] The calculation of the separation factor as a function of theactivity coefficient was published by Gmehling and Brehm [Gmehling, J.and Brehm, A., Grundoperationen (Unit Operations), ISBN 3-13-687401-3,chapter 3].

[0144] Accordingly, the additive interacts more vigorously with butenethan with butane. The powerful effect exhibited by the ionic liquidOMIM-BF₄ on the phase equilibrium of the binary butene-butane systemdemonstrates the suitability of OMIM-BF₄ as an entrainer for separatingalkanes and alkenes.

EXAMPLE 2 System to be Separated: Cyclohexanol-cyclohexanone

[0145] According to the literature [Gmehling, J, Onken, U and Arlt, WVapor-Liquid Equilibrium Data Collection, Dechema Data Series, Vol. IPart 2b, p. 403] the cyclohexanol-cyclohexanone system is aclose-boiling system.

[0146] The separation factor which was measured by means of gas-liquidchromatography at infinite dilution of cyclohexanol and cyclohexanone inthe ionic liquids ethylmethylimidazolium tetrafluoroborate (EMIM-BF₄)and ethylmethylimidazolium hexafluorophosphate (EMIM-PF₆) is 1.66 at142° C. for EMIM-BF₄ and 1.61 at 140.8° C. for EMIM-PF₆. Both ionicliquids bring about an increase in the separation factor of thecyclohexanol-cyclohexanone separation system and are thus suitable asentrainers.

EXAMPLE 3 System to be Separated: Acetone-methanol

[0147] According to the literature [Gmehling, J, Onken, U and Arlt, WVapor-Liquid Equilibrium Data Collection, Dechema Data Series, Vol. IPart 2a, p. 75] the acetone-methanol system forms an azeotrope. Theseparation factor for a mixture of a ketone and an alcohol, acetone andmethanol in this case, was determined by means of GLC in infinitedilution in the ionic liquids EMIM-BF₄, OMIM-BF₄, MMIM-CH₃SO₄,EMIM-(CF₃SO₂)₂N and EMIM-PF₆. These experiments yielded a separationfactor of 2.51 at 70° C. for EMIM-BF₄, of 3.15 at 70° C. for OMIM-BF₄,of 1.3 at 70.5° C. for MMIM-CH₃SO₄, of 0.5 at 84.6° C. forEMIM-(CF₃SO₂)₂N and of 0.67 at 70° C. for EMIM-PF₆. From these resultsit may be seen that it is not just isolated ionic liquids that aresuitable as entrainers. On the contrary, many members of this novelclass of substances, the ionic liquids, are suitable for use asentrainers.

[0148] The process according to the invention is explained below bymeans of further examples in which headspace analysis is used.

EXAMPLE 4 Effect of the Ionic Liquid 1-ethyl-3-methylimidazoliumTetrafluoroborate on the Binary Homoazeotropic System Ethanol-water

[0149] Table 1 shows the effect of the additive (entrainer)1-ethyl-3-methylimidazolium tetrafluoroborate on the binaryethanol-water system at θ=70° C. and a molar liquid concentration of theentrainer of 10 mol % and 50 mol %. TABLE 1 Separation factor α of thebinary, homoazeotropic system ethanol-water at 70° C. using differentquantities of the ionic liquid 1-ethyl-3-methylimidazoliumtetrafluoroborate ^(α)Ethanol, ^(α)Ethanol, ^(α)Ethanol, ^(α)Ethanol,Water Water Water Water ternary system ternary system ternary systembinary containing containing containing system 10 mol % 50 mol % 70 mol% without entrainer of entrainer of entrainer of entrainer ^(x)Ethanol^(x)Water according to according to according to according to [mol %][mol %] the invention the invention the invention the invention 0.100.90 7.12 4.64 5.74 6.23 0.20 0.80 4.45 3.90 5.49 6.11 0.30 0.70 2.993.25 5.17 6.00 0.40 0.60 2.37 2.70 4.77 5.86 0.50 0.50 1.88 2.41 4.575.72 0.60 0.40 1.58 2.12 4.38 5.58 0.70 0.30 1.34 1.85 4.20 5.25 0.800.20 1.17 1.68 4.02 4.95 0.90 0.10 1.06 1.48 3.99 4.90 0.95 0.05 1.001.32 3.56 4.87

[0150] The ethanol-water azeotrope occurs at approximatelyx_(Ethanol)=0.95. It is precisely in the range around this that theentrainer has an effect, even at a concentration of 10 mol % in theliquid phase. The fact that in this and in the following examples ahigher separation factor is achieved in the peripheral region withoutentrainer than with entrainer is not disadvantageous since:

[0151] a) preliminary concentration can be carried out withoutentrainer;

[0152] b) separation factors about>5 approximately have virtually noinfluence on operating and capital costs.

EXAMPLE 5 Effect of the Ionic Liquid 1-ethyl-3-methylimidazoliumTetrafluoroborate on the Binary Homoazeotropic SystemTetrahydrofuran-water

[0153] Table 2 shows the effect of the entrainer1-ethyl-3-methylimidazolium tetrafluoroborate on the binarytetrahydrofuran (THF)-water system at 70° C. and a molar liquidconcentration of the entrainer of 50 mol %. TABLE 2 Separation factor αof the homoazeotropic system tetrahydrofuran (THF)-water at 70° C. withand without the ionic liquid 1-ethyl-3-methylimidazoliumtetrafluoroborate ^(α)THF, Water ^(α)THF, Water ternary binary systemwithout system containing 50 mol % ^(X)THF ^(X)Water entrainer accordingof entrainer according to [mol %] [mol %] to the invention the invention0.10 0.90 25.54 18.09 0.20 0.80 12.38 16.73 0.30 0.70 7.97 15.37 0.400.60 5.59 14.01 0.50 0.50 3.87 12.65 0.60 0.40 2.56 11.29 0.70 0.30 1.649.93 0.80 0.20 1.10 8.57 0.90 0.10 0.79 7.21

[0154] The azeotrope at values of x_(THF) between 0.8 and 0.9 isimpressively removed.

EXAMPLE 5a Effect of the Ionic Liquid 1-ethyl-3-methylimidazoliumTetrafluorotosylate on the Binary Homoazeotropic SystemTetrahydrofuran-water

[0155] Table 2a shows the effect of the entrainer1-ethyl-3-methylimidazolium tetrafluorotosylate on the binarytetrahydrofuran (THF)-water system at a pressure of 1 bar and a molarliquid concentration of the entrainer of 50 mol %. TABLE 2a Separationfactor α of the tetrahydrofuran (THF)-water system at 1 bar with theionic liquid 1-ethyl-3-methylimidazolium tetrafluorotosylate. Themeasured results shown here were not obtained by headspacechromatography but rather by means of an equilibrium apparatus. Herealso a distinct increase in the separation factor relative to the binarysystem (see Table 2) and hence the suitability of the ionic fluid asentrainer may be seen. ^(α)THF, Water ^(X)THF ^(X)Water ternary systemcontaining 50% [mol %] [mol %] of entrainer according to the invention0.2459 0.7541 23.3 0.3843 0.6157 24.7 0.5355 0.4645 23.8 0.6307 0.369322.8

EXAMPLE 6 Effect of the Ionic Liquid 1-ethyl-3-methylimidazoliumTetrafluoroborate on the Binary Homoazeotropic System Propanol-water

[0156] Table 3 shows the effect of the entrainer1-ethyl-3-methylimidazolium tetrafluoroborate on the binarypropanol-water system at 85° C. and a molar liquid concentration of theentrainer of 50 mol %. TABLE 3 Separation factor α of the homoazeotropicsystem propanol-water at 85° C. with and without the ionic liquid1-ethyl-3-methylimidazolium tetrafluoroborate ^(α)Propanol, Waterternary ^(α)Propanol, system containing Water binary system 50 mol % of^(X)Propanol ^(X)Water without entrainer entrainer according [Mol %][Mol %] according to the invention to the invention 0.4 0.6 1.10 3.120.6 0.4 0.68 2.46

EXAMPLE 7 Effect of the Ionic Liquid 1-ethyl-3-methylimidazoliumTetrafluoroborate on the Binary Homoazeotropic System Isopropanol-water

[0157] Table 4 shows the effect of the entrainer1-ethyl-3-methylimidazolium tetrafluoroborate on the binaryisopropanol-water system at 90° C. and a molar liquid concentration ofthe entrainer of 50 mol %. TABLE 4 Separation factor α of thehomoazeotropic system isopropanol-water at 90° C. with and without theionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate^(α)Isopropanol, Water ternary ^(α)Isopropanol, Water system containingbinary system without 50 mol % of ^(X)Isopropanol ^(X)Water entraineraccording entrainer according [Mol %] [Mol %] to the invention to theinvention 0.4 0.6 2.09 5.73 0.6 0.4 1.29 4.64

[0158] In Tables 1 to 4 a marked difference is discernible between thebinary phase compositions and the ternary phase equilibrium compositionsformed after addition of the nonvolatile entrainer according to theinvention 1-ethyl-3-methylimidazolium tetrafluoroborate. Due toselective interactions with the polar system component, water, the ionicliquid exercises an advantageous effect on the separation factor.Moreover, in the ethanol-water (Table 1) and tetrahydrofuran-water(Table 2) systems it is clearly evident that the effect of the ionicliquid on the vapor-liquid phase equilibrium is so great that theazeotropic point has been broken down, that is to say it no longeroccurs.

EXAMPLE 8 Advantage of the Entrainer According to the Invention Relativeto Conventional Entrainers with Reference to the Example of theSeparation of Ethanol and Water

[0159] Table 5 shows for the ethanol-water system the effect of the twoentrainers 1-ethyl-3-methylimidazolium tetrafluoroborate and ethanediolon the vapor-liquid phase equilibrium at 70° C. for the entrainerconcentration of 50 mol %. TABLE 5 Comparison of the separation factorsα in the ethanol-water system at 70° C. for the conventional entrainerethanediol and the entrainer according to the invention1-ethyl-3-methylimidazolium tetrafluoroborate ^(α)Ethanol, Water^(α)Ethanol, ^(α)Ethanol, ternary system Water binary Water containingsystem without ternary system 50 mol % entrainer containing of entrainer^(X)Ethanol ^(X)Water according 50 mol % according to [mol %] [mol %] tothe invention of ethanediol the invention 0.10 0.90 7.12 4.96 5.74 0.200.80 4.45 4.37 5.49 0.30 0.70 2.99 3.77 5.17 0.40 0.60 2.37 3.45 4.770.50 0.50 1.88 3.14 4.57 0.60 0.40 1.58 2.82 4.38 0.70 0.30 1.34 2.634.20 0.80 0.20 1.17 2.44 4.02 0.90 0.10 1.06 1.83 3.99 0.95 0.05 1.001.32 3.56

[0160] From Table 5 it emerges that for the same concentration ofentrainer the effect on the vapor-liquid phase equilibrium and hence theuseful effect is distinctly greater in the case of the ionic liquid,particularly in the azeotropic range.

What is claimed is:
 1. A process for separating liquids or condensable gases in the condensed state comprising: use of an entrainer which is an ionic liquid and brings about a change in the separation factor of the components to be separated divergent from one; the ionic liquid being present at a total concentration of 5 to 90 mol %, preferably 10 to 70 mol % in the liquid phase.
 2. A method as claimed in claim 1, comprising the separation being carried out by means of extractive rectification in a column wherein: the low-boiling component or components under the conditions of claim 1 are obtained at the top of the column while all other components are obtained as bottom product together with said entrainer at the bottom of the column, the liquid mixture at the bottom of the column (bottom product and entrainer) is worked up in such a way that said entrainer can be recovered and the components of the bottom product are obtained as a further fraction, the column is operated in countercurrent flow, said entrainer is introduced into the column above the feed of the components to be separated.
 3. The method as claimed in claim 2, wherein the separation of said bottom product from said entrainer is carried out by evaporation in evaporators or in rectification columns.
 4. The method as claimed in claim 2, wherein the work-up of the mixture of bottom product and entrainer ensues by precipitation of the component which has the higher freezing point.
 5. The method as claimed in claim 2, wherein the separation of said bottom product from said entrainer is effected by drying.
 6. The method as claimed in claim 2, wherein the separation of said bottom product from said entrainer is effected by extraction.
 7. The method as claimed in claim 2, wherein no separative elements are needed above the point of admission of said entrainer into the extractive rectification system.
 8. The process as claimed in claim 1, wherein the feed is a water-containing system which in addition to water contains alcohols having a carbon number between 1 and 12, preferably between 1 and 8, particularly preferably between 1 and 5, organic acids, preferably alkanoic acids, ketones, furans and separation of the water from the other substances is achieved.
 9. The process as claimed in claim 1, wherein said feed contains alkanes and alkenes having a carbon number between 3 and 12, preferably between 4 and 10 and separation between alkanes and alkenes is achieved.
 10. The process as claimed in claim 1, wherein said feed contains aromatic and aliphatic hydrocarbons and separation between aromatics and aliphatics is achieved.
 11. The process as claimed in claim 1, wherein said feed contains ketones and alicyclic compounds and the ketones are separated from the alicyclic components.
 12. The process as claimed in claim 1, wherein said feed contains amides and acids, preferably carboxylic acids, and the amides are separated from the acids.
 13. The process as claimed in claim 1, wherein said feed contains alcohols and alkanes and the alkanes are separated from the alcohols.
 14. The process as claimed in claim 1, wherein said feed contains alcohols and aromatics and the alcohols are separated from the aromatics.
 15. The process as claimed in claim 1, wherein said feed contains ketones and alcohols and the ketones are separated from the alcohols.
 16. The process as claimed in claim 1, wherein said feed contains acetates and ketones and the acetates are separated from the ketones.
 17. The process as claimed in claim 1, wherein said feed contains ethers and alkanes and the ethers are separated from the alkanes.
 18. The process as claimed in claim 1, wherein said feed contains ethers and alkenes and the ethers are separated from the alkenes.
 19. The process as claimed in claim 1, wherein said feed contains sulfides and ketones and the sulfides are separated from the ketones.
 20. The process as claimed in claim 1, wherein said feed contains halogenated hydrocarbons and ketones and the halogenated hydrocarbons are separated from the ketones.
 21. The process as claimed in claim 15, wherein said feed contains cyclic ketones and/or cyclic alcohols and these are separated from one another.
 22. The process as claimed in claim 1, wherein the anion of said ionic liquid used as said entrainer is a metallic halide.
 23. The process as claimed in claim 1, wherein said ionic liquid used as said entrainer has an anion such as the nitrate anion or the tetrachloroaluminate anion or the tetrafluoroborate anion or the heptachlorodialuminate anion or the hexafluorophosphate anion or the methylsulfate anion or pure halide anions.
 24. The process as claimed in claim 1, wherein said ionic liquid used as said entrainer has a cation such as the imidazolium cation or the pyridinium cation or the ammonium cation or the phosphonium cation.
 25. The process as claimed.in claim 1, wherein mixtures of ionic liquids are used as said entrainer.
 26. A method, wherein the process as claimed in claims 1 and 8 to 25 is carried out and implemented in accordance with claims 2 to
 7. 27. Products which are separated in accordance with claims 1 to
 26. 28. The method as claimed in claim 2, wherein the separation of said bottom product from said entrainer is effected by means of stripping using an inert gas. 